Several methods and apparatus have been developed for laying pipe underwater. When pipe is laid in deep water, it must be supported at intermediate positions along its length. One particular support apparatus and method, to which this invention pertains, involves a freely articulated stinger, i.e. a stinger free to pivot in at least the vertical plane, to lay pipe. Each such articulated stinger, according to prior apparatus and methods, provides structural support for pipe at intermediate points along the pipe path, and in the immediate vicinity of the pipelaying vessel.
A typical articulated stinger, such as that shown and described in Broussard et al. U.S. Pat. No. 3,438,213, comprises a plurality of pipe guiding elements, stinger elements, which are pivotably connected end to end so that they may pivot at least in a vertical plane. The articulated stinger is connected to a pipelaying vessel for pivotal movement in at least the vertical plane.
Aboard the vessel, sections of pipe are assembled and payed out onto the stinger assembly. The inclination and depth of the stinger assembly along its length is controlled by adjusting the buoyancy of the individual stinger elements, for example, by appropriate air and/or water content variations in the various elongated tubular components of the stinger. Wave action, however, at or near the surface of the water, tends to cause both the pipelaying barge and the articulated stinger attached thereto, at or near the water surface to move with the water fluctuations. As a result, out-of-phase movement between the vessel, the pipe and the stinger which supports the submerged pipe away from the vessel, can develop. When the relative movement between a portion of the stinger assembly and the corresponding portion of pipe are out of phase, banging between the pipe and the stinger can occur. In the extreme, severe banging may cause pipeline and/or stinger damage to occur.
It is therefore an object of this invention to provide an improved articulated stinger apparatus in which banging between the stinger apparatus and the pipe is substantially reduced, in which the first structural support for the pipe is at a depth below that at which effective wave action occurs, and wherein the pipe is unsupported for a significant distance beyond the last support on the pipelaying vessel.
Other objects of the invention include providing an articulated stinger assembly in which the first section is non-articulated and is substantially longer than each of the succeeding sections and in which the first support point for the pipe is near the connection point between a first extended, non-articulated stinger link and a buoyant stinger means and beneath the level of effective wave action.